Re: What exactly is objectionable?
" It also seems fair that, to be paid for a piece of work, you should hand that work over to the company paying you."
That's a bit the wrong way around. They don't pay someone to do some work. They reward someone who does work for them for free and has a good enough relationship that they won't exploit this work or hand it over to crims or TLAs for an even bigger fee.
The security researchers see it as doing the company a favour and hence getting a reward, the company may see it as an extortion racket (but it's only due to their failings).
However if the agreement to be given the reward for your hard work is unfair or gives too much power to the company to shut you down and keep others at risk for ever more and even not pay you at all once you've signed it then you might be a bit irked.
In another way if you have 30 top security researchers who are very bothersome with their constant stories about security issues and you can get them all to sign an NDA which says they are not allowed to mention a security bug ever again (and they might get a rewards, maybe) then you have shut down dissent and you can carry on with insecure software.
I was genuinely considering buying a DJI drone but stories like this where they don't seem to care about security and prefer to try to ensure that issues aren't rectified they are suppressed mean that I won't risk it.